"Killing Floor is a Co-op Survival Horror FPS set in the devastated cities and countryside of England after a series of cloning experiments for the military goes horribly wrong. You and your friends are members of the military dropped into these locations with a simple mission: Survive long enough to cleanse the area of the failed experiments!" -Steam
I picked up Killing Floor a while back after it had a free weekend. My first impressions were great. I generally don't play 'scary' games, but Killing Floor is an exception. It's a game that keeps making you come back for more. And it rewards you for coming back, with its class system. There are seven different classes in the game, and each have unique passive bonuses and are more adept at different weapon classes. The more you use a class, the more experienced you become with it, unlocking extra/more powerful bonuses.
From the KF Wiki: "The Firebug is primarily a supporting class, specializing in mob control. His main task is to ignite groups of specimens early to help thin out the smaller zeds, while softening up larger targets and making them easier to deal with. To accomplish this, the Firebug utilizes fire-based damage, receiving bonuses for the Flamethrower, MAC-10, Trenchgun, Husk fireball launcher, and (with a DLC purchase) the Flare Revolver. For all of the five weapons, the Firebug is given a damage bonus of up to 60%, a discount of up to 70%, increased ammo capacity of up to 60%, and faster reload speed (with the exception of the Husk fireball launcher, which doesn't reload)."
The other six classes are the Field Medic (PDW's such as the MP7/MP5 that can heal other players), Support Specialist (Shotguns), Sharpshooter (Pistols and long-range weapons such as the M14 and Crossbow), Commando (Assault Rifles), Berzerker (Melee), and Demolition (Explosives).
The game features both solo and multiplayer games, which are round-based, and five different levels of difficulty, ranging from Beginner to Hell on Earth. There are 10 unique zombies, including Clots, the cannon fodder of the game, Stalkers, which are fast-moving and can turn invisible, and Scrakes, large and dangerous zombies wielding chainsaws with deadly efficiency.
There are many diverse maps, one the most popular being West London: A smaller map on the rundown and zombie-infested streets of London. There are also event maps such as Santa's Evil Lair and the Abusement Park. On special holiday events, all of the zombies are reskinned to represent the holiday, and they are generally very well done.
I definitely recommend this game (why else would I be writing about it) to anyone who favors survival, horror, or FPS games. It's a very successful mix of the genres, and you can pick it up on Steam for just $19.99. There is some paid DLC in the game, though only a small portion includes extra guns. Most of the DLC is extra costumes.
Happy killing!
--DarkestMagi